LARGE technology firms used to hold on to their high-flying employees by agreeing not to poach them from each other. “If you hire a single one of these people, that means war,” Steve Jobs, Apple’s then boss, warned Sergey Brin, a founder of Google, in 2005. That was an illegal arrangement, and in 2015 Apple, Google, Adobe and Intel paid a $415m settlement to engineers whose pay had been held down as a result.

Today wage suppression in Silicon Valley is even more of a distant memory...